One type of optical reflection modulator is known from German Patent Publication DE 40 31 970. In the arrangement disclosed in the German Patent Publication, light exiting the blunt end of an optical fiber strikes a mirror disposed orthogonally to the fiber. This mirror reflects the light back onto itself, thus creating a standing wave in the manner of a Fabry-Perot resonator between the reflecting fiber end and the mirror, provided their distance from each other corresponds to a multiple of half a wavelength of the light used. By changing the distance between the reflecting fiber end and the mirror, particularly by displacing the mirror, the Fabry-Perot resonator can be detuned and the intensity of the light can be changed.
The described modulator is of a relatively simple design and has good modulating properties. However, it is dependent on the absolute value of the distance between the fiber end and the mirror, which changes because of many effects, for example, as a function of the temperature. It is therefore necessary to provide a regulator which maintains the "optical distance" between the reflecting fiber end and the mirror constant.
There is thus a need for a light modulator having modulating properties comparable to those of prior devices, but which does not require maintaining a length constant. There is also a need for a highly sensitive light modulator which is nevertheless of a simple design. There is also a need to achieve these ends in a modulator of the species of optical reflection modulators with movable mirror surfaces.